Phil Mickelson will not resign from the PGA Tour and has confirmed he intends to take part in next week's U.S. Open, despite his LIV Golf Invitational Series involvement.

The 51-year-old will end a four-month self-imposed exile from golf on Thursday when the inaugural LIV Golf event gets underway at Centurion Club on the outskirts of London.

Mickelson was met with widespread condemnation after criticising the PGA Tour earlier this year, for which he apologised and vowed to take a step back from the game.

That saw the six-time major champion miss The Masters and the defence of his US PGA Championship, though he is still registered to play at the upcoming U.S. Open.

And while Mickelson refused to confirm whether he has been serving a PGA Tour ban for his controversial comments, he will not voluntarily quit the American circuit.

"I've been a part of the tour for over 30 years and I've had a lot of incredible memories and experiences, tournaments that I've won and lost," he said on Wednesday.

"I've gained a lot, received a lot and I'm grateful for everything the tour has done for me. I've also worked hard to contribute and build and add value to the tour in my time there.

"I worked hard to get a lifetime exemption. I don't want to give that up. I don't feel I should have to. 

"I don't know what's going to happen. I've earned that and I don't plan on just giving it up.

"I've really enjoyed my time on the PGA Tour. I've had some incredible experiences, great memories and I have a lot of strong opinions that it should and could be a lot better. 

"One mistake I've made is voicing them publicly. I will make an effort to keep those conversations behind closed doors moving forward."

Mickelson then confirmed he will compete in next week's U.S. Open in Massachusetts and added: "I'm looking forward to it."

The United States Golf Association, which runs the major, has already announced it will not stop those competing in the LIV Golf series from playing at The Country Club.

Unlike Mickelson, others taking part in the Saudi-backed breakaway LIV Golf circuit – such as Dustin Johnson and Sergio Garcia – have resigned from the PGA Tour.

"I saw that and I think they're making the decision that's best for them personally," Mickelson said.

"I respect that. As a lifetime member I'm not required to play 15 events. I don't have to play any. I can play one. So I don't see a reason for me to give that up."

Mickelson is reported to have been given a $200million signing-on fee to appear in LIV Golf events, but he refused to be drawn on the specifics during a tense news conference.

"Contract agreements should remain private," he said.